The present invention relates to a spray gumming unit.
The invention can be used to good advantage in the field of packaging machinery, especially packing machines, to which the description below refers but without thereby restricting the scope of the invention.
In these machines, an adhesive substance must be applied to certain parts of paper sheets, such as blanks, for example, designed to be folded into containers or packets, or labels to be applied to the containers or packets.
Packing machines are known to be equipped with spray gumming units facing the line along which the paper sheets to be gummed are fed, each unit comprising at least one spray gummer whose gumming nozzle is connected to an adhesive feed system and is equipped with an adhesive ejector.
The disadvantage of spray gumming units of this type is that the gumming nozzle ejectors require frequent cleaning and maintenance, mainly because part of the adhesive dries on the ejectors during temporary stops in production.
To overcome this problem, the ejectors of the gumming units have been equipped with shutter elements that move towards and away from the ejectors between a position where the ejectors are closed and in which pads fixed to one end of the shutter elements are placed in contact with the ejectors, and a position where the ejectors are left open and an antiadhesive liquid substance is applied manually on the pads in order to prevent the pads and the adhesive from sticking in the closed position.
Obviously, a solution of this kind has the disadvantage of requiring the constant attendance of an operator to apply the antiadhesive substance on the pads.
The aim of the present invention is to provide a spray gumming unit that overcomes the disadvantage just described.
Accordingly, the invention provides a spray gumming unit, having at least one spray gummer with a gumming nozzle equipped with an adhesive ejector; the unit also having shutter means designed to keep the ejector closed during stops in gumming operations, said shutter means moving towards and away from the ejector, during such stops, between an ejector open position and an ejector closed position; and drive means for moving the shutter means between such open and closed positions; the unit being characterized in that it comprises applicator means for applying a liquid substance on a working portion of the shutter means as the shutter means themselves move between the open and closed positions.